Introduction

Mysmenids are one of the least studied groups of orb-weaving spiders, mainly because of their minuscule size (0.6-3 mm; Fig. 1) and cryptic life history. The family Mysmenidae is distributed worldwide, and with only around 100 described species, the diversity of mysmenids is clearly under-sampled as numerous undescribed species of this family have been collected and/or exist in museum collections around the world.

Mysmenids live mainly in leaf litter and other cryptic places in humid habitats. Mysmenid web-spinning species seem to usually prefer the interstices of leaf litter and small cavities about 5-15 cm in diameter (depending on the size of the spider) created by the top layer of leaves. They can be collected by beating foliage, using pitfall traps, Berlese funnels, Winkler devices (e.g. Wheeler and McHugh, 1987), or just manually.

Only a few mysmenid spiders have been documented from the fossil record (eight species in five genera). Seven fossil mysmenids have been described from Tertiary ambers from the Miocene (15–20 Ma; two species from Dominican amber), Miocene–Oligocene (19–27 Ma, one species from Chiapas amber), and Eocene (44 Ma, two species from the Baltic amber, and two species from the Baltic and Bitterfeld ambers). A relatively recent species was described from Madagascan copal (a semi-fossilized resin less than two million years old).

Characteristics

Mysmenids resemble some theridiids in their somatic morphology, as well as some members of the more closely related symphytognathoid families (Anapidae, Symphytognathidae, Theridiosomatidae and Synaphridae).

Male mysmenids can be distinguished from other araneoids by the presence of a metatarsal clasping spine on the first legs (Fig. 2) and by a particular composition and arrangement of their copulatory organs (palps, Fig. 3). Females have a distinct dark modification, like a spot, on the apical ventral surface of at least the first femur (Fig. 4, sometimes on the second femur and in some species such modification is also present in males). Both sexes of mysmenids have the anterior median eyes on a protruding area (or all eyes on tubercle); a prolateral row of modified setae on the first tarsus (Fig. 2); a distinctly thicker and curved seta on the chelicerae; and denticles in the cheliceral fang furrow (Fig. 5).

Very little is known about the biology and natural history of mysmenids. Eleven species in three mysmenid genera have been reported to be kleptoparasites on the webs of other spiders, such as diplurids, tengellids, or lycosoids. The webs of most other mysmenids have never been documented. Mysmenids are known to build two main types of web architecture. Mysmena and Microdipoena species build highly modified three-dimensional spherical-shaped orb webs. In contrast, the webs of Maymena species are mainly planar but the central hub is distorted upwards by one to several radial lines that attach to substrate above the web. Members of the symphytognathoid family Anapidae build webs identical to the ones built by Maymena species.

Discussion of Phylogenetic Relationships

After more than 80 years since the erection of the family, the first generic-level cladistic analysis of Mysmenidae is in progress (Lopardo and Hormiga, in prep.). This combined analysis using morphological and molecular data will test the monophyly of the family and its genera, and will also hypothesize a placement of Mysmenidae within the Symphytognathoidea. Until now the placement of Mysmenidae within this group has been based exclusively on morphology and behavior. Two cladistic analyses included mysmenids in the past (Griswold et al., 1998; Schütt 2003) and, to a limited extent, tested the monophyly of the family. These two analyses included only two mysmenid representatives. Both placed the Mysmenidae within Symphytognathoidea, either as sister to Symphytognathidae, or to a clade comprising Anapidae plus Symphytognathidae. More recently, a new phylogenetic hypothesis for Araneoidea and Symphytognathoidea has been proposed (Lopardo and Hormiga, 2008), revising and expanding some of the previous phylogenetic work. Lopardo and Hormiga (2008) placed Mysmenidae either as sister to the clade comprising Anapidae and Symphytognathidae (as originally proposed by Griswold et al., 1998) or as sister to Theridiosomatidae. Only two molecular phylogenetic analyses have included mysmenid representatives, as part of the outgroup taxa (Arnedo et al., 2004; Rix et al., 2008).

References

Arnedo, M, Coddington, J, Agnarsson, I and Gillespie, R. 2004. From a comb to a tree: Phylogenetic relationships of the comb-footed spiders (Araneae, Theridiidae) inferred from nuclear and mitochondrial genes. Molecular Phylogenetics and Evolution 31: 225-245.

Brescovit, A and Lopardo, L. 2008. The first record on the spider genus Trogloneta Simon in the southern hemisphere (Araneae, Mysmenidae), with descriptions of three new species from Brazil and remarks on the morphology. Acta Zoologica (Stockholm) 89: 93–106.

Lopardo, L, Dupérré, N and Paquin, P. 2008. Expanding horizons... The first report of the genus Mysmena (Araneae, Mysmenidae) from continental North America, with the description of a new species. Zootaxa 1718: 36–44.

Wunderlich, J. 2004. The fossil spiders of the family Anapidae s. l. (Aeaneae) [sic] in Baltic, Dominican and Mexican amber and their extant relatives, with the description of the new subfamily Comarominae. Beiträge zur Araneologie 3: 1020-1111.

Page: Tree of Life
Mysmenidae.
Authored by
Lara Lopardo and Gustavo Hormiga.
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